com.avaje.ebean.annotation

Annotation Type Formula

@Target(value={FIELD,METHOD,TYPE})
@Retention(value=RUNTIME)
public @interface Formula

Assign to a property to be based on a SQL formula.

This is typically a SQL Literal value, SQL case statement, SQL function or similar.

Any property based on a formula becomes a read only property.

You may also put use the Transient annotation with the Formula annotation. The effect of the Transient annotation in this case is that the formula will NOT be included in queries by default - you have to explicitly include it via Query.select(String) or Query#join(String, String). You may want to do this if the Formula is relatively expensive and only want it included in the query when you explicitly state it.

 // On the Order "master" bean
 // ... a formula using the Order details
 // ... sum(order_qty*unit_price)
 @Transient
 @Formula(select = "_b${ta}.total_amount", join = "join (select order_id, sum(order_qty*unit_price) as total_amount from o_order_detail group by order_id) as _b${ta} on _b${ta}.order_id = ${ta}.id")
 Double totalAmount;
 
 

As the totalAmount formula is also Transient it is not included by default in queries - it needs to be explicitly included.

 // find by Id
 Order o1 = Ebean.find(Order.class)
     .select("id, totalAmount")
     .setId(1).findUnique();
 
 // find list ... using totalAmount in the where clause
 List<Order> list = Ebean.find(Order.class)
     .select("id, totalAmount")
     .where()
     .eq("status", Order.Status.NEW)
     .gt("totalAmount", 10)
     .findList();
 
 // as a join from customer
 List<Customer> l0 = Ebean.find(Customer.class)
     .select("id, name")
     .join("orders", "status, totalAmount")
     .where()
     .gt("id", 0)
     .gt("orders.totalAmount", 10)
     .findList();
 
 

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
String	select The SQL to be used in the SELECT part of the SQL to populate a property.

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
String	join OPTIONAL - the SQL to be used in the JOIN part of the SQL to support the formula.

Element Detail

select

public abstract String select

The SQL to be used in the SELECT part of the SQL to populate a property.

join

public abstract String join

OPTIONAL - the SQL to be used in the JOIN part of the SQL to support the formula.

This is commonly used to join a 'dynamic view' to support aggregation such as count, sum etc.

The join string should start with either "left outer join" or "join".

You will almost certainly use the "${ta}" as a place holder for the table alias of the table you are joining back to (the "base table" of the entity bean).

The example below is used to support a total count of topics created by a user.

 join (select user_id, count(*) as topic_count from f_topic group by user_id) as _tc on _tc.user_id = ${ta}.id
 

Default:

""